python / python/mypy

"# E:" lines (etc) in test files are ignored at the beginning of lines

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Description

As discovered in the unrelated https://github.com/python/mypy/pull/19494#discussion_r2243899624, "# E:" lines (etc) in test files are ignored at the beginning of lines. Having looked at the code, I've discovered this is because it desires the # to be preceded by a space, which is not present when the # is at the beginning of a line. This is bad because attempted error lines should not be silently ignored. (Although it is unlikely for someone to try to E an empty line.)

My PR #19546 will fix this. Edit: that would still be true, but #21172 is a much more minimal fix for this.

Easy repro:

[case testErrorCodeOnEmptyLine]
# E: This isn't a real message, and thus this test could never pass, although somehow it currently does :)

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First steps

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  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
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Research direction

Start with mypy/test/data.py around line 536 and reproduce the behavior using the test case shown in the issue. Compare the proposed minimal fix in issue #21172, since the body says the broader approach in PR #19546 is no longer preferred. Done means the invalid beginning-of-line “# E:” assertion is no longer silently ignored.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
testing-qa
Issue type
Bug
Difficulty
2/5
Estimated time
1-3 hours
Activity status
Stale
Clarity
Clearly specified
Newbie friendliness
20/100

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